In the past, a vehicle-mounted radar apparatus derives a position of a target. The derivation of the position of the target is performed as follows. A transmission wave outputted from a transmission antenna of the radar apparatus is reflected from the target. A reflection wave reflected from the target is received by a reception antenna of the radar apparatus.
The radar apparatus derives a distance (hereinafter referred to a vertical distance) of the target with respect to the radar apparatus based on a time difference until the reflection wave is received after the transmission wave is outputted. Further, the radar apparatus derives a vehicle width distance (hereinafter referred to as a horizontal distance) of the target and the radar apparatus based on an angle of the target with respect to the radar apparatus. That is, the radar apparatus derives a position of a horizontal direction of the target with respect to a road surface from the vertical distance and the horizontal distance of the target. Further, the radar apparatus derives a relative speed of the other vehicle with respect to the vehicle.
The target derived by the radar apparatus is, for example, the other vehicle (hereinafter referred to the other vehicle) existing at the substantially same height as the vehicle in a direction perpendicular to the road surface. The radar apparatus outputs the position of the target in a horizontal direction and the relative speed to a vehicle control device. As a result, the vehicle control device performs various vehicle controls based on the position of the target in a horizontal direction and the relative speed.
The vehicle control device performs plural types of vehicle controls. An example of the vehicle control includes ACC (Adaptive Cruise Control) control and PCS (Pre-Crash Safety System) control. The ACC control is a control of driving the vehicle CR to follow up the other vehicle (hereinafter referred to as a preceding vehicle) driving ahead the vehicle in a state in which a given inter-vehicular distance between the vehicle and the preceding vehicle is retained. The PCS control is a control of protecting a passenger of the vehicle against an impact when collision occurs.
Since the vehicle control device is primarily intended to follow up the preceding vehicle in order to perform the ACC control, the radar apparatus preferably performs distant beam radiation at a relatively narrow angle. For example, it is required to output the transmission wave in a transmission range within a predetermined vertical distance (within about 150 m of vertical distance) while the horizontal distance is within a self-lane (within about ±1.8 m of horizontal distance). The about ±1.8 m of the horizontal distance is a distance of the self-lane in the vehicle width direction. In other words, it is a distance of the vehicle width direction in which the width of the self-lane is set to about 3.6 m and the position of the radar apparatus is set to ±0 m of the horizontal direction.
Further, since it is necessary to detect a possibility of collision against an object positioned obliquely in front of the vehicle, as well as facing directly forward, to allow the vehicle control device to perform the PCS control on the vehicle, the radar apparatus preferably performs a close-range beam radiation in the relatively wide range. For example, it is required to output the transmission wave in the transmission range within the predetermined vertical distance (within about 80 m of vertical distance) while the horizontal distance is within about ±7.2 m. About ±7.2 m of the horizontal distance is a distance of the vehicle width direction including the self-lane and any one of left and right traffic lanes adjacent to the self-lane. In other words, it is a distance of the vehicle width direction in which each width of the traffic lane adjacent to the self-lane is set to about 3.6 m, and the position of the radar apparatus is set to ±0 m of the horizontal distance.
Also, the radar apparatus may derive the vertical distance and the horizontal distance of a substance (e.g., a sign) above a road having a certain height (e.g., about 4.5 m) in a direction perpendicular to the road surface, except for the other vehicle on the road surface. If the substance above the road is derived, the radar apparatus outputs the position of the horizontal direction and the relative speed to the vehicle control device. As a result, in a case where the vertical distance of the substance above the road with respect to the vehicle is equal to or less than a predetermined distance, the vehicle control device may perform the PCS control, for example. However, the substance above the road is a target having a little risk of collision against the vehicle even though the vertical distance with respect to the vehicle is shorter. For this reason, the substance above the road is a target having no necessity for the vehicle control by the vehicle control device. Therefore, the radar apparatus is required to derive an angle of the target in a direction perpendicular to the road surface to discriminate the target and the target having a certain height in direction perpendicular to the road surface.
In the case where the vehicle control device performs plural types of vehicle controls, a transmission range suitable for each control is required. For this reason, the antenna of the radar apparatus is necessarily provided with a plurality of transmission antennas having different transmission ranges. Further, in a case where the radar apparatus derives the angle of the target in the horizontal direction and the vertical direction with respect to the road surface, the reception antenna is considered to be arranged in the horizontal direction and the vertical direction with respect to a substrate surface of a dielectric substrate. In this instance, a technique for the arrangement of the reception antenna is disclosed in Patent Document 1.    Patent Document 1: Japanese Patent Application Publication No. H11-287857A
However, the number of the reception antennas provided in the antenna of the radar apparatus is increased to derive the angle of the target in the horizontal direction and the vertical direction with respect to the road surface, thereby remarkably increasing an area of the antenna in which the transmission antenna and the reception antenna are arranged. Further, in the case of increasing the number of the transmission antennas to allow the vehicle control device to perform plural types of vehicle controls, the area of the antenna is further increased.
With the increase in area of the antenna, the radar apparatus itself including the antenna is increased in size. If the radar apparatus grows in size, it is difficult to mount the radar apparatus to a limited mounting space of the vehicle.